In conventional gas turbines, acoustic oscillation usually occurs in the combustion chamber of the gas turbines during combustion process due to combustion instability and varieties. This acoustic oscillation may evolve into highly pronounced resonance. Such oscillation, which is also known as combustion chamber pulsations, can assume amplitudes and associated pressure fluctuations that subject the combustion chamber itself to severe mechanical loads that my decisively reduce the life of the combustion chamber and, in the worst case, may even lead to destruction of the combustion chamber.
Generally, a type of damper known as Helmholtz damper is utilized to damp the resonance generated in the combustion chamber of the gas turbine.
A damper arrangement is disclosed in EP2397760A1, which comprises a first damper connected in series to a second damper that is separated by a piston from the first damper, wherein the resonance frequency of the first damper is close to that of the second damper. A first neck interconnects the damping volumes of the first and second damper. A rod is connected to the piston to regulate the damping volumes of the first and second damper.
A damper is disclosed in US2005/0103018A1, which comprises a damping volume that is composed of a fixed damping volume and a variable damping volume. The fixed and variable damping volumes are separated by a piston, which may be displaced by means of an adjust element in the form of a thread rod. If the adjustment element is rotated, the piston moves along the cylinder axis of the damping volume and can adopt various positions. The frequency at which the damping occurs or reaches its maximum also changes correspondingly with the damping volumes.
One type of conventional Helmholtz damper features multiple damping volumes to provide a broadband damping efficiency. Individual volumes are interconnected with small plain tubes, i.e. so-called inner necks. Usually, the mean flow velocity in the inner neck is higher than that of the main neck connecting the damper to the combustion chamber. Especially for high-frequency dampers with small geometrical dimensions, the flow coming out of the inner necks either shoots into the main neck if the inner and main neck are placed coaxially or it impinges on an opposite structural components resulting in complicated flow fields. This can result in a dramatic decrease of damping efficiency. In addition, if the damper is tunable, the damper features a movable spacer plate or exchangeable necks to adjust the damper to the respective pulsation frequencies, where the damping characteristic is strongly dependent on the resulting flow fields. Position varieties of the spacer plate in the damper corresponds to different flow fields, which makes it not possible to set up the acoustic models to derive the damper design for a robust performance.